Quantitative evaluation of the expression and activity of five major sulfotransferases (SULTs) in human tissues: the SULT "pie"

Abstract

Expression levels of the major human sulfotransferases (SULTs) involved in xenobiotic detoxification in a range of human tissues (i.e., SULT "pies") are not available in a form allowing comparison between tissues and individuals. Here we have determined, by quantitative immunoblotting, expression levels for the five principal human SULTs-SULT1A1, SULT1A3/4, SULT1B1, SULT1E1, and SULT2A1-and determined the kinetic properties toward probe substrates, where available, for these enzymes in cytosol samples from a bank of adult human liver, small intestine, kidney, and lung. We produced new isoform-selective antibodies against SULT1B1 and SULT2A1, which were used alongside antibodies against SULT1A3 and SULT1A1 previously produced in our laboratory or available commercially (SULT1E1). Expression levels were derived using purified recombinant enzymes to construct standard curves for each individual isoform and immunoblot. Substantial intertissue and interindividual differences in expression were observed. SULT1A1 was the major enzyme (>50% of total, range 420-4900 ng/mg cytosol protein) in the liver, followed by SULT2A1, SULT1B1, and SULT1E1. SULT1A3 was completely absent from this tissue. In contrast, the small intestine contained the largest overall amount of SULT of any of the tissues, with SULT1B1 the major enzyme (36%), closely followed by SULT1A3 (31%), and SULT1A1, SULT1E1, and SULT2A1 more minor forms (19, 8, and 6% of total, respectively). The kidney and lung contained low levels of SULT. We provide a unique data set that will add value to the study of the role and contribution of sulfation to drug and xenobiotic metabolism in humans.

Figures

Fig. 1.

Immunoblot demonstrating anti-SULT antibody specificity and representative standard curves. Cytosols prepared from a number of liver (A–D) or duodenum (E) samples were resolved on SDS-PAGE gels, along with the appropriate purified human SULTs diluted as necessary to construct the standard curves. Following transfer to polyvinylidene difluoride membranes, blots were immunostained with the corresponding anti-SULT antibody and secondary antibody as listed in Table 2.

Fig. 2.

Expression of SULTs in human tissues expressed as a percentage of levels in the small intestine. Mean expression level data are expressed relative to the mean values obtained with the small intestinal cytosols (shown as 100%) because this was the only tissue in which all five enzymes were detected.

Fig. 3.

The human SULT pies. The mean expression values for each enzyme are displayed as percentages of the total sum of immunoquantified SULTs (maximum five enzymes) present in each tissue. Expression values are shown for liver (A), small intestine (B), kidney (C), and lung (D).